共沉淀法制备钕掺杂钛酸铋粉体

以硝酸铋、钛酸丁酯和硝酸钕为原料采用共沉淀法制备掺钕钛酸铋粉体.用X射线衍射(XRD)和透射电镜(TEM)对所得粉体进行了表征.以甲基橙为目标降解物,借助紫外一可见分光光度计考察了样品的光催化性能.结果表明:钕掺杂对BT晶体的结构没有影响,但钕在BT中的溶解度有限.钕掺杂能提高BT的光催化性能,当钕掺杂量为0.35时B...     

Low-Temperature Synthesis of Bismuth Titanate by an Aqueous Sol–Gel Method

Homogeneous and fine bismuth titanate (BIT) nanoplate-like powders were synthesized by a modified and simple sol–gel method. The thermal gravimetry-differential thermal analysis-derivative differential thermal analysis indicated that BIT gel decomposes in two steps posited at approximately 278° and 432°C, and BIT began to crystallize before 450°C. Based on the high-temperature X-ray diffraction results, it was concluded that the crystallization temperature of BIT synthesized by the present method was about 425°C and there was no evidence of the formation of an intermediate phase. The BIT crystal structure belonged to the orthorhombic phase with lattice parameters a =5.420 Å, b =5.431 Å, and c =33.273 Å. Field emission-scanning electron microscopy revealed that fine and uniform BIT nanoplate-like powders, about 30 nm in size, were obtained after sintering at 500°C. With increasing temperature, the BIT grains rapidly grew and the coalescence of adjacent grains took place. The synthesis temperatures adopted were substantially lower than those reported in the other literatures.     

Hydrothermal Synthesis of Ferroelectric Mixed Potassium Niobate–Lead Titanate Nanoparticles

Potassium niobate–lead titanate solid‐solution nanoparticles have been synthesized using a new hydrothermal method. The key step is an in situ acid–base exothermic reaction with a large excess of KOH, generating an amorphous precipitated gel. This gel, when crystallized in an autoclave for 2 h at 190°C, produces a mixed perovskite solid solution with [KNbO₃]_0.8–[PbTiO₃]_0.2 (KNPT) composition, and parallelepiped particles rang in size from a few tens to a few hundreds of nanometer in length. This study proves that the pure perovskite phase can be obtained in spite of the different solubilities of the reactive cations in an ethanol–water solution. Dielectric measurements show that KNPT ceramic with a grain size of 50 nm is ferroelectric at room temperature. In addition, ceramics sintered at 950°C have an average grain size of 500 nm, and exhibit a maximum permittivity of 2100 at 1 kHz near T_C = 510 K and a remanent polarization P_r = 12 μC/cm²     

Hydrothermal Synthesis of Bismuth Titanate Powders

Bismuth titanate was synthesized under hydrothermal conditions from an amorphous bismuth–titanium precursor gel. The gel was formed by mixing a bismuth acetate complex with titanium butoxide and then adding the solution dropwise into 6 M NaOH. The resulting gel suspension was reacted under hydrothermal conditions at temperatures ranging from 160° to 200°C to form crystalline bismuth titanate. The gel crystallization kinetics increased with temperature, which resulted in 100% crystalline bismuth titanate in 5 h at 200°C. Wavelength-dispersive spectroscopy data indicated that sodium was incorporated into bismuth titanate during processing, and X-ray diffractometry suggested that the powder was composed of the Bi₅Ti₄O₁₅ phase. Transmission electron microscopy micrographs showed that the gel particles decomposed to 100–200 nm crystalline bismuth titanate particles during hydrothermal processing.     

Synthesis of Highly Dispersed Barium Titanate Nanoparticles by a Novel Solvothermal Method

A novel solvothermal route has been developed to synthesize highly dispersed nanocrystalline barium titanate (BaTiO₃), using a mixture of ethylenediamine and ethanolamine as a solvent. The as-synthesized BaTiO₃ nanoparticles were characterized by X-ray powder diffraction, transmission electron microscopy (TEM), high-resolution TEM, Fourier transform infrared spectroscopy, and thermal analysis. Based on the results of characterizations, the organic solvent was found to influence strongly the crystal growth and dispersibility of BaTiO₃. The BaTiO₃ nanoparticles obtained were highly dispersed and crystalline with a cubic perovskite structure. The particle size derived from the TEM ranged from 5 to 20 nm.     

Low-Temperature Synthesis of Zinc Oxide Nanoparticles

Crystalline zinc oxide nanoparticles have been prepared by mixing aqueous solutions of zinc nitrate and hexamethylenetetramine (HMT) at 60°C and 80°C. Transmission electron microscopy and X-ray diffraction show that the ZnO nanoparticles of diameters ranging from 15–33 nm and 25–43 nm long are formed. Aspect ratio is observed to range from 1.18 to 1.74 at 60°C and 1.22 to 1.70 at 80°C as the HMT to zinc nitrate concentration ratio increases from 10 to 150. Nanoparticle size decreases as the concentration of HMT increases. Much larger ZnO particles are formed with ammonium hydroxide as a hydrolysis agent without HMT. In summary, HMT is an ammonium-hydroxide source in the reaction, a surfactant for retaining nanosize, and not necessarily a template for ZnO nucleation.     

分子筛负载钛酸铋光催化剂的制备及性能研究

采用溶胶-凝胶法制备粉末Bi4Ti3O12光催化剂,研究煅烧温度、煅烧时间对其活性的影响,确定了Bi4Ti3O12的制备条件。将HZSM-5作为载体,采用机械混合和溶胶-凝胶法制备负载型χBi4Ti3O12/HZSM-5催化剂。结果表明,700℃下煅烧5 h的Bi4Ti3O12活性最高;与HZSM-5机械混合使Bi4Ti3O12活性略有降低;HZSM-5抑制溶胶-凝胶法合成Bi4Ti3O12,导致其活性显著下降。     

Low-Temperature Synthesis of Nanosized Bismuth Ferrite by Soft Chemical Route

The present research describes a simple low-temperature synthesis route of preparing bismuth ferrite nanopowders through soft chemical route using nitrates of Bismuth and Iron. Tartaric acid is used as a template material and nitric acid as an oxidizing agent. The synthesized powders are characterized by X-ray diffractometry, thermogravimetry and differential thermal analysis, infrared spectroscopy, and scanning electron microscopy. The particle size of the powder lies between 3 and 16 nm. In the process, phase pure bismuth ferrite can be obtained at a temperature as low as 400°C, in contrast to 550°C for coprecipitation route. On the other hand, we find that, like solid state reaction route, Pechini's autocombustion method of synthesis generates a lot of impurity phases along with bismuth ferrite.     

Mo掺杂调控钛酸铋钠铁电陶瓷带隙的实验与第一性原理研究

为改善钛酸铋钠基无铅陶瓷的铁电光伏特性,通过传统固相法制备了B位Mo掺杂的Na0.5 Bi0.5(Ti1-x Mox)O3(BNT-Mox,x=0～0.02)无铅铁电陶瓷.通过XRD、拉曼光谱、吸收光谱等测试方法,结合基于密度泛函理论的第一性原理计算,研究了Mo掺杂对BNT陶瓷体系带隙的影响规律及机理.结果表明:随着M...     

Ferroelectric Properties of Lead Titanate

The eutectic and solidus temperatures of the PbTiO₃-KF binary system were investigated by DTA for four compositions. Optical studies of crystal habit as a function of crystallization conditions were used to determine favorable conditions for growing PbTiO₃ crystals from a KF flux. Results of X-ray studies of these crystals agree closely with those of earlier studies. Interferometric measurements of thermal expansion confirmed the ferroelectric transition at 490° C. Specific heat studies indicated a transition energy of about 1550 cal/mole with an entropy change of 2.055 cal/mole °C. Spontaneous polarization was calculated as 66 μcoulombs/cm².     

Synthesis of Ferroelectric Lead Titanate Nanohoneycomb Arrays via Lead Supplement Process

Here, we demonstrate a novel process to convert TiO₂ nanotubes into ferroelectric nanohoneycombs, comprised of vertically aligned PbTiO₃ nanotubes. Tube bottom opening process enabled effective infiltration of lead acetate precursor into the nanotubes. Nanohoneycombs, which were converted via additional lead supplement process, showed uniform conversion and well‐defined ferroelectric properties with the effective piezoelectric coefficient of approximately 20 pm/V, which was measured by piezoresponse force microscopy.     

Low-Temperature Synthesis, Characterization, and Properties of Lead-Based Ferroelectric Niobates

Technologically important lead-based ferroelectric niobates of the type A(B'B)O₃ (where A is Pb, B' is Fe, Ni, Mg, or Zn, and B is Nb), and their solid solutions with barium titanate and lead titanate, have been prepared via a solution combustion process that involves metal nitrates/oxalate and tetraformal trisazine (TFTA) at a temperature of 350°C. The thermal evolution of perovskite niobates has been investigated at different calcination temperatures. Particulate properties such as density, particle size, and surface area have been determined. Particles are fine (<1 µm) and are sinter active at low temperature (1050°C). Dielectric and piezoelectric properties of the lead-based ferroelectrics that have been prepared via the low-temperature method are reported in this paper.     

Barium Zirconate-Lead Titanate Ferroelectric Ceramics

Hot-pressed barium zirconate-lead titanate ceramics have been examined to determine crystal-line symmetry and dielectric, ferroelectric, and piezoelectric properties. Barium zirconate additions to lead titanate form solid solutions with a decreasing tetragonal c/a axial ratio until at 60PbTiO₃–40BaZrO₃ to 75PbTiO₃–25BaZrO₃ the ceramics have coercive forces low enough to permit polarization. High-coercive-force piezo-electric ceramics are formed with k_p up to 0.30 and d₃₃ up to 110 × 10⁻¹² coulombs per newton.     

La2Mo2O9掺杂钛酸铋钠铁电陶瓷的微观结构与光电性能

铁电陶瓷的极化内建电场可分离光生载流子并有效降低载流子间的复合率,但是其高带隙限制了对光的吸收.本文以具有良好铁电性能的Bi0.5 Na0.5 TiO3(BNT)陶瓷为基体,通过掺杂La2 Mo2 O9降低光学带隙,提高光电流密度.样品使用传统固相法制备,随后分析了此陶瓷的XRD、拉曼、光吸收、光电流、铁电和介电性质....     

Low-Temperature Synthesis of Nanocrystalline Zinc Titanate Materials with High Specific Surface Area

Nanocrystalline zinc titanate (ZnTiO₃) was synthesized at low temperatures through the combination of a sol–gel processing and a polymer binder method. ZnTiO₃ powders of ∼5 nm in size were obtained by heating pastes, which were composed of a Zn-Ti methanolic solution containing acetylacetone and an organic polymer binder, at 500°C in air. Thermal decomposition behavior of the pastes was analyzed by thermogravimetry-differential thermal analysis. Crystallinity of ZnTiO₃ was examined by transmission electron microscopy. The BET measurement revealed that the powders had a relatively high specific surface area of 106 m²/g.     

Low-Temperature Synthesis of Bismuth Titanate Niobate (Bi7Ti4NbO21) Nanoparticles from a Metal-organic Polymeric Precursor

This paper describes the preparation of homogeneous Bi₇Ti₄NbO₂₁ single-phase ceramic powders of ∼55 nm crystallite size, at temperatures as low as 400°–500°C using a metal citrate complex method based on the Pechini-type reaction route. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, and SEM, led to the formation of a well-defined orthorhombic Bi₇Ti₄NbO₂₁ compound with lattice parameters a = 0.544, b = 0.540, and c = 2.905 ± 0.0005 nm. Reaction takes place through an intermediate binary phase with a stoichiometry close to Bi₂₀TiO₃₂ which forms between 300° and 375°C. The metal-organic precursor synthesis method, where Bi, Ti, and Nb ions are first chelated to form metal complexes and then polymerized to give a gel, allows control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of nanosized bismuth titanate niobate (Bi₇Ti₄NbO₂₁) ceramic powders, at temperatures much lower than usually needed by conventional processing of mixed-oxide powders.     

Aging in Tetragonal Ferroelectric Barium Titanate

The aging phenomenon in tetragonal ferroelectric bairum titanate was investigated by optical microscopy and by electrical measurements. Transmission electron microscopy was used to observe in detail domain reactions which occurred during aging. Aging may be characterized as an exhaustion-type process because of the increase in the apparent activation energy with time. It is concluded that aging is the relief of the residual stresses of the ferroelectric transition by the thermally activated nucleation of 90° domains.     

A Novel Low-Temperature Synthesis of Nanosized NiZn Ferrite

Nanosized NiZn ferrite powder is synthesized by a low-temperature method, using a unique combination of citric acid and glycine. An appropriate molar ratio of both citric acid and glycine offers a low-temperature synthetic route by incorporating the complexation behavior of citric acid and the combustion nature of glycine. Thermal decomposition/controlled autocatalytic combustion of the composite gel occurs at a low temperature of around 175°C, with the evolution of a large amount of gases. Transmission electron microscopic studies showed that the average particle size of the ferrite obtained is ∼2.5 nm, with a narrow size distribution. Uniformly distributed fine-grained microstructure with low porosity is obtained for a sample sintered at 1000°C.     

Synthesis and Characterization of Bismuth Titanate by an Aqueous Sol–Gel Method

A highly stable, reproducible and water-based bismuth titanate (BTO) sol system has been synthesized by an aqueous sol–gel method. First bismuth nitrate was dissolved in acetic acid, and then it was mixed with a solution of lactic acid dissolved tetra- n -butyl titanate, subsequently, water was added to adjust sol concentration. As-obtained sols or gels were characterized by Ultraviolet–Visible Spectrophotometer, derivative differential thermal analysis-differential thermal analysis–thermal gravimetry, in situ Raman, and high-temperature X-ray diffraction. Results show that the BTO sol can remain stable for more than 1 year and BTO can start to crystallize at about 450°C.     

Spark Plasma Sintering of Bismuth Titanate Ceramics

Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi₄Ti₃O₁₂) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi³⁺ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi₄Ti₃O₁₂ ceramics.